MR imaging perfusion and diffusion analysis to assess preoperative Short Course Radiotherapy response in locally advanced rectal cancer: Standardized Index of Shape by DCE-MRI and intravoxel incoherent motion-derived parameters by DW-MRI.

Our aim is to assess preoperative Short Course Radiotherapy (SCR) tumor response in locally advanced rectal cancer (LARC) through Standardized Index of Shape (SIS) by DCE-MRI, apparent diffusion coefficient (ADC) and intravoxel incoherent motion-derived parameters by DW-MRI. 35 patients with LARC underwent MR scan before and after SCR followed by delayed surgery, retrospectively, were enrolled. SIS, ADC, tissue diffusion (D t), pseudodiffusion (D p), and perfusion fraction (f) were extracted by MRI for each patient before and after SCR. Tumor regression grade (TRG) was estimated. Receiver operating characteristic curve and linear classification were performed. Sixteen patients were classified as responders (TRG ≤ 2) and 19 as non-responders. Seven patients had TRG1 [pathological complete response (pCR)]. The best parameter to discriminate responders by non-responders was SIS (sensitivity 94%, specificity 84%, accuracy 89%, cutoff value = - 7.8%). SIS obtained the best diagnostic performance also to discriminate pCR (sensitivity 86%, specificity 89%, accuracy 89%, cutoff value = 68.2%). No accuracy increase was obtained combining linearly each possible parameters couple or all functional MR-derived parameters. SIS is a hopeful DCE-MRI angiogenic biomarker to assess preoperative treatment response after SCR with delayed surgery, and it permits to discriminate pCR allowing to direct surgery for tailored and conservative treatment.